1. Field of the Invention
This invention relates to improvement in heating technique used in heat-refining process of petroleum high-molecular hydrocarbons.
In particular, this invention relates to a method for reducing remarkably deposition of cokes which are produced heating units used in heat-refining process of petroleum high-molecular hydrocarbons, by incorporating an additive for reducing deposition of cokes in the petroleum high-molecular hydrocarbons.
This invention relates also to the additive for reducing deposition of coke in the petroleum high-molecular hydrocarbons.
This invention also relates to a novel use of a compound (I) having at least one mercaprtoalkylthio group: HS--C.sub.m H.sub.2m --S--, in which "m" is an integer of 2 to 4.
2. Description of Related Art
One of objects of oil refinery is to increase the yield of lighter components such as kerosene and gas oil which are much value added products comparing to heavier components which are less value added products. In fact, in actual oil refinery processes, heavier components such as residual oil from atmospheric distillation column is heat-treated in vacuum distillation column, thermal cracking unit or visbreaking unit to obtain lighter components. These processes and apparatuses are well-known and are described in many books, for example "World Encyclopedia" 13, Heibon-sha, 1966, p 237-254.
The yield of lighter components can be increased by elevating operation temperature in the heating units. However, elevation of operation temperature in the heating units cause a trouble of increment of cokes which deposit on inner walls of heating unit or heat-exchangers, resulting in frequent stop of production plants for maintenance. In particular, in a case of thermal cracking process of heavy oil, heating tubes in a heating furnace are seriously contaminated and are choked with deposited cokes, so that production plant can not be operated continuously but must be stopped frequently for cleaning.
Due to this problem, actual oil refinery plants are compelled to be operated at lower operation temperature than such ideal operation temperature that assure higher yield of lighter components. In other words, operation temperature can not be elevated above certain limit.
Inventors found, surprisingly, such a fact that deposition of cokes can be reduced remarkably by incorporating an additive having speific mercapto alkylthio group in material of petroleum high-molecular hydrocarbons to be refined in heating units used in a variety of oil refining processes, and completed the invention.